Detroit SO2 Nonattainment Area Redesignation to Attainment

Content

ACTION:

Final rule.

SUMMARY:

The Environmental Protection Agency (EPA) is finding that the Detroit, Michigan area is attaining the 2010 sulfur dioxide
(SO 2) National Ambient Air Quality Standard (NAAQS) and is acting in accordance with a request from the Michigan Department of
Environment, Great Lakes, and Energy (EGLE) to redesignate the area to attainment for the 2010 SO 2 NAAQS, because the request meets the statutory requirements for redesignation under the Clean Air Act (CAA). The EPA is also
approving Michigan's maintenance plan for the Detroit area. Michigan submitted the request for approval of the Detroit nonattainment
area's redesignation and maintenance plan on May 5, 2025. The EPA approved Michigan's attainment plan for the Detroit area
on May 19, 2025.

DATES:

This final rule is effective on April 2, 2026.

ADDRESSES:

The EPA has established a docket for this action under Docket ID No. EPA-R05-OAR-2025-0238. All documents in the docket are
listed on the https://www.regulations.gov website. Although listed in the index, some information is not publicly available, i.e., Confidential Business Information (CBI), Proprietary Business Information (PBI), or other information whose disclosure is
restricted by statute. Certain other material, such as copyrighted material, is not placed on the internet and will be publicly
available only in hard copy form. Publicly available docket materials are available either through https://www.regulations.gov or please contact the person identified in the
FOR FURTHER INFORMATION CONTACT
section for additional information.

FOR FURTHER INFORMATION CONTACT:

Alexis Bender, Air and Radiation Division (AR-18J), Environmental Protection Agency, Region 5, 77 West Jackson Boulevard,
Chicago, Illinois 60604, telephone number: (312) 886-9497, email address: bender.alexis@epa.gov.

SUPPLEMENTARY INFORMATION:

Throughout this document whenever “we,” “us,” or “our” is used, we mean the EPA.

I. Background Information

On August 5, 2013 (78 FR 47191), the EPA designated the Detroit area, a portion of Wayne County, Michigan, as nonattainment
for the 2010 SO 2 NAAQS. On May 19, 2025 (90 FR 21228), the EPA approved Michigan's plan for attaining the 2010 SO 2 NAAQS for the Detroit area and for meeting other nonattainment area planning requirements of CAA sections 110, 172, 179 and
192. On August 14, 2025 (90 FR 39148), the EPA proposed to approve Michigan's redesignation request and maintenance plan for
the Detroit nonattainment area for the 2010 SO 2 NAAQS.

II. Response to Comments

Upon publication of the August 14, 2025 (90 FR 39148), proposed rulemaking, the EPA opened a 30-day comment period, ending
September 15, 2025. The EPA received one adverse comment, which is summarized below along with the EPA's response. The comment
is included in the docket for this action.

Comment: The commenter suggests that there is insufficient evidence to demonstrate attainment in the Detroit area. Wayne County, in
partnership with JustAir, has placed 100 air sensors in the county that have shown an average SO 2 level of 14.5 parts per billion (ppb) from May 1, 2024, when they began operation, to June 30, 2025. The commenter argues
that the JustAir monitoring network demonstrates a

  more granular measure of air quality than the five regulatory SO 2 monitors that Michigan EGLE operates in the Detroit area. While the commenter concedes that preliminary data from the JustAir *sensors* shows SO 2 levels below the primary SO 2 standard, the commenter suggests that the JustAir *sensors* have captured values that could indicate an exceedance of the recently revised secondary SO 2 standard. Additionally, the commenter states that the attainment demonstration relies on modeling using maximum allowable
  emissions but does not provide robust evidence that the applicable facilities are complying with the emission limits and associated
  requirements included in the plan.

Response: The reference to the secondary SO 2 standard is outside of the scope of this action, as this action is only addressing the primary standard for SO 2. For monitoring compliance with the NAAQS, the EPA utilizes an appendix of the CAA to address the requirements for monitoring
quality assurance. The appendix, 40 CFR part 58 appendix A, specifies the minimum quality system requirements applicable to
State and Local Monitoring Stations and other monitor types used to determine compliance with the NAAQS. The appendix addresses
quality system requirements, measurement quality check requirements, calculations for data quality assessments, and reporting
requirements. Therefore, the JustAir monitoring program, which does not follow this appendix, is not a reliable source of
data for comparison to the NAAQS.

With regard to modeling using maximum allowable emissions, the EPA's April 23, 2014, “Guidance for 1-Hour SO 2 Nonattainment Area SIP Submissions” states that the EPA may make determinations of attainment based on the modeling, using
allowable emissions, from the attainment demonstrations for the applicable SIP for the affected area. For a short-term (i.e., 1-hour) standard, the EPA believes that dispersion modeling, using allowable emissions and addressing stationary sources in
the affected area (and in some cases those sources located outside the nonattainment area which may affect attainment in the
area) is technically appropriate, efficient and effective in demonstrating attainment in nonattainment areas because it takes
into consideration combinations of meteorological and emission source operating conditions that may contribute to peak ground-level
concentrations of SO 2. In reality, it is extremely unlikely that all sources would be operating at maximum emission rates simultaneously. The Detroit
area met all compliance dates in Michigan's plan, and Michigan included compliance documentation as appendix D of its May
5, 2025, redesignation request, which is included in the docket for this action. Additionally, Michigan has shown that it
maintains an active enforcement program to ensure ongoing compliance with the requirements included in the Detroit attainment
plan.

Comment: The commenter raises concern that the primary 1-hour SO 2 NAAQS was set to protect against short-term SO 2 exposure and does not reflect long-term exposure risks. The commenter states that Wayne County residents have experienced
health impacts from long-term, low-level exposure to SO 2, which the primary 1-hour standard does not address.

Response: Under section 109 of the CAA, the EPA sets primary, or health-based, NAAQS for all criteria pollutants to provide requisite
protection of public health, including the health of at-risk populations, with an adequate margin of safety. In the EPA's
June 22, 2010 (75 FR 35520), rulemaking strengthening the SO 2 NAAQS to the level of 75 ppb, the EPA provided a detailed rationale for the Administrator's determination that the 2010 SO 2 NAAQS would be protective of public health. This rationale included explicit consideration of protection for people, including
children, with asthma. Specifically, the standard was based on direct evidence of SO 2 -related effects in controlled human exposure studies of exercising individuals with asthma, as well as epidemiologic evidence
of associations between SO 2 concentrations in ambient air and respiratory-related emergency department visits and hospitalizations. This action does not
address the primary SO 2 NAAQS itself but rather recognizes that the Detroit area has achieved the primary SO 2 NAAQS.

Comment: The commenter raises concerns over the potential for increased pollution from facilities within the Detroit area, citing that
redesignating the area to attainment risks signaling that efforts to reduce emissions are no longer a priority. The commenter
states that the decreased SO 2 levels in the Detroit area suggest that the current nonattainment status of the area has successfully led to lower pollution
in the area and removing the enhanced scrutiny and enforcement measures that come with nonattainment status may lead to increased
emissions. Additionally, the commenter contends that the measures put forth by Michigan within the maintenance plan for the
area are reactive rather than preventative, as contingency measures would be triggered only after exceedances occur. Therefore,
the commenter suggests that the maintenance plan should contain proactive measures that would be triggered at the first signs
of SO 2 increases.

Response: A redesignation to attainment does not remove any emission control measures for existing sources that are already adopted
into the EPA approved SIP for Michigan. As discussed in the proposal for this action, Michigan's redesignation request includes
a demonstration that attainment of the SO 2 NAAQS was attributable to permanent and enforceable emissions reductions. Further, Michigan's redesignation request includes
a plan to maintain the SO 2 NAAQS, which includes an attainment emission inventory, a maintenance demonstration, a commitment for continued air quality
monitoring, a process for verification of continued attainment, and a contingency plan, which all will support measures to
ensure the Detroit area remains in attainment and does not violate the SO 2 NAAQS in the future.

In the “General Preamble for the Implementation of Title I of the Clean Air Act Amendments of 1990,” published on April 16,
1992 (57 FR 13498), the EPA provides discussion of contingency measures specifically for SO 2. This guidance states that in many cases, attainment revolves around compliance of a single source or a small set of sources
with emission limits shown to provide for attainment. Although this guidance applies to contingency measures under section
172(c)(9), the EPA applies a similar policy with respect to contingency measures for SO 2 required in maintenance plans under section 175A(d). The requirement to submit contingency measures in accordance with section
175A of the CAA can be adequately addressed for SO 2 by the operation of a comprehensive enforcement program, which can quickly identify and address sources that might be causing
exceedances of the NAAQS.

As discussed in the proposal, Michigan has demonstrated that it maintains a comprehensive and active enforcement program capable
of prompt action to remedy compliance issues. Beyond this, as part of its contingency plan, Michigan commits to adopt and
expeditiously implement necessary corrective actions in the event of a violation of the standard, or if an annual 99th percentile
daily maximum 1-hour SO 2 concentration of 79 ppb or above

  occurs in a single calendar year in the Detroit area.

Comment: The commenter states that the attainment framework does not adequately capture the cumulative impacts of long-term exposure
to pollution. The commenter states that residents living in the Detroit area are disproportionately exposed to environmental
hazards, including SO 2 and other pollutants. The commenter also notes that SO 2 can react in the atmosphere to form particulate matter and argues that elevated levels of SO 2 could lead to health effects from both exposure to SO 2 and particulate matter.

Response: The EPA is committed to protecting human health. For all criteria pollutants, the EPA ensures that the NAAQS are set to provide
an adequate margin of safety for both the general population and susceptible populations that are potentially at increased
risk for health effects in response to exposure to ambient air pollution.

When considering the primary SO 2 NAAQS, the EPA took into account the Integrated Science Assessment (ISA) of scientific information on known and potential
human health effects associated with exposure to SO 2 in the air via the (1) Assessments in the Risk and Exposure Assessment (REA) of the most policy-relevant information in the
ISA as well as quantitative exposure and risk analyses based on that information; (2) Clean Air Scientific Advisory Committee
(CASAC) Panel advice and recommendations, as reflected in its letters to the Administrator and its public discussions of the
ISA and REA; (3) public comments received during the development of the ISA and REA; and (4) public comments received on the
EPA's notice of proposed rulemaking. Additionally, the EPA referred to the ISA regarding health effects and long-term exposures
to SO 2 which addressed and concluded the long-term health evidence to be of insufficient quantity, quality, consistency, or statistical
power to make a determination as to whether SO 2 was truly associated with these health outcomes. Therefore, when strengthening the SO 2 standard, the EPA drew upon an entire body of evidence on human health effects associated with the presence of SO 2 in the ambient air, and upon the results of the quantitative exposure and risk assessments reflecting this evidence.

In this action, the EPA is recognizing that the Detroit area has achieved the primary SO 2 NAAQS and is approving Michigan's maintenance plan for the area. While the EPA appreciates the commenter's concerns regarding
other pollutants in the Detroit area, the EPA is not evaluating the air quality in the Detroit area with respect to other
NAAQS in this action.

III. What action is the EPA taking?

The EPA is redesignating the Detroit area from nonattainment to attainment for the 2010 SO 2 NAAQS in accordance with Michigan's May 5, 2025, request. The EPA has determined that the area is attaining the 2010 SO 2 NAAQS and that the improvement in air quality is due to permanent and enforceable SO 2 emission reductions in the area. The EPA is also approving Michigan's maintenance plan, which is designed to ensure that the
area will continue to maintain the 2010 SO 2 NAAQS.

In accordance with 5 U.S.C. 553(d) of the Administrative Procedure Act (APA), this action shall become effective immediately
upon publication. The immediate effective date for this action is authorized under 5 U.S.C. 553(d)(1).

Section 553(d)(1) of the APA provides that final rules shall not become effective until 30 days after publication in the
Federal Register
“except . . . a substantive rule which grants or recognizes an exemption or relieves a restriction.” The purpose of this provision
is to “give affected parties a reasonable time to adjust their behavior before the final rule takes effect.” Omnipoint Corp. v. Fed. Commc'n Comm'n, 78 F.3d 620, 630 (D.C. Cir. 1996); see also United States v. Gavrilovic, 551 F.2d 1099, 1104 (8th Cir. 1977) (quoting legislative history). However, when the agency grants or recognizes an exemption
or relieves a restriction, affected parties do not need a reasonable time to adjust because the effect is not adverse. The
EPA has determined that this rule relieves a restriction because this rule relieves sources in the area of Nonattainment New
Source Review permitting requirements; instead, upon the effective date of this action, sources will be subject to less restrictive
Prevention of Significant Deterioration permitting requirements. For this reason, the EPA finds that under 5 U.S.C. 553(d)(1)
it is appropriate for this action to become effective on the date of publication of this action.

IV. Statutory and Executive Order Reviews

Under the CAA, redesignation of an area to attainment and the accompanying approval of a maintenance plan under section 107(d)(3)(E)
are actions that affect the status of a geographical area and do not impose any additional regulatory requirements on sources
beyond those imposed by state law. A redesignation to attainment does not in and of itself create any new requirements, but
rather results in the applicability of requirements contained in the CAA for areas that have been redesignated to attainment.
Moreover, the Administrator is required to approve a SIP submission that complies with the provisions of the CAA and applicable
Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, the EPA's role is to approve
State choices, provided that they meet the criteria of the CAA. Accordingly, this action merely approves State law as meeting
Federal requirements and does not impose additional requirements beyond those imposed by State law. For that reason, this
action:

• Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Order 12866 (58 FR 51735, October 4, 1993);
• Is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025) because SIP actions are exempt from review under Executive Order 12866; • Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);

• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory
Flexibility Act (5 U.S.C. 601 et seq.);

• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);
• Does not have federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);
• Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because it approves a State program;
• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and
• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA. In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where the EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction. In those areas of Indian country, the rule does not have Tribal implications and will not impose substantial direct costs on Tribal governments or preempt Tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).

This action is subject to the Congressional Review Act, and the EPA will submit a rule report to each House of the Congress
and to the Comptroller General of the United States. This action is not a “major rule” as defined by 5 U.S.C. 804(2).

Under section 307(b)(1) of the CAA, petitions for judicial review of this action must be filed in the United States Court
of Appeals for the appropriate circuit by June 1, 2026. Filing a petition for reconsideration by the Administrator of this
final rule does not affect the finality of this action for the purposes of judicial review nor does it extend the time within
which a petition for judicial review may be filed, and shall not postpone the effectiveness of such rule or action. This action
may not be challenged later in proceedings to enforce its requirements. (See section 307(b)(2).)

List of Subjects

Environmental protection, Air pollution control, Incorporation by reference, Intergovernmental relations, Reporting and recordkeeping
requirements, Sulfur oxides.

Environmental protection, Air pollution control, National parks, Wilderness areas.

Dated: March 26, 2026. Anne Vogel, Regional Administrator, Region 5. For the reasons stated in the preamble, title 40 CFR parts 52 and 81 are amended as follows:

PART 52—APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS

Regulatory Text 1. The authority citation for part 52 continues to read as follows:

Authority:

42 U.S.C. 7401 et seq.

1. In § 52.1170, the table in paragraph (e) is amended under “Maintenance Plans” by adding an entry for “2010 SO 2 ” after the entry for “2008 lead (Pb)” to read as follows:

§ 52.1170 Identification of plan.

---

(e) * * *

| Name of nonregulatory SIP provision | Applicable geographic or nonattainment area | State submittal date | EPA approval date | Comments |
| --- | --- | --- | --- | --- |
| | | | | |
|                                                       * | | | | |
| Maintenance Plans | | | | |
| | | | | |
|                                                       * | | | | |
| 2010 SO
2 | Detroit area (Wayne County, part) | 5/5/2025 | 4/2/2026, 91 FR [INSERT
FEDERAL REGISTER
PAGE WHERE THE DOCUMENT BEGINS] | |
| | | | | |
|                                                       * | | | | |

PART 81—DESIGNATION OF AREAS FOR AIR QUALITY PLANNING PURPOSES

Regulatory Text 3. The authority citation for part 81 continues to read as follows:

Authority:

42 U.S.C. 7401 et seq.

1. In § 81.323, the table entitled “Michigan-2010 Sulfur Dioxide NAAQS [Primary]” is amended by revising the entry for “Detroit, MI” to read as follows:

§ 81.323 Michigan.

---

| Designated area 
1 | Designation | |
| --- | --- | |
| Date 2 | Type | |
| Detroit, MI | 4/2/2026 | Attainment. |
| Wayne County (part) | | |
| The area bounded on the east by the Michigan-Ontario border, on the south by the Wayne County-Monroe County border, on the
west by Interstate 75 north to Southfield Road, Southfield Road to Interstate 94, and Interstate 94 north to Michigan Avenue,
and on the north by Michigan Avenue to Woodward Avenue and a line on Woodward Avenue extended to the Michigan-Ontario border | | |
| | | |
|                                                       * | | |
| 1 Includes any Indian country in each county or area, unless otherwise specified. EPA is not determining the boundaries of
any area of Indian country in this table, including any area of Indian country located in the larger designation area. The
inclusion of any Indian country in the designation area is not a determination that the state has regulatory authority under
the Clean Air Act for such Indian country. | | |
| 2 This date is April 9, 2018, unless otherwise noted. | | |

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[FR Doc. 2026-06396 Filed 4-1-26; 8:45 am] BILLING CODE 6560-50-P

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